It is proposed to study the presence of IgG-rheumatoid factor (IgG-RF) and IgM-rheumatoid factor (IgM-RF) in the serum and synovial fluid of patients with rheumatoid arthritis (RA). The distribution of IgG-RF in the density gradient fractions of RA serum will also be measured. The synthesis of these factors by RA synovial tissue will be measured in addition. The factors regulating the synthesis of IgM-RF by RA peripheral blood mononuclear cells (PBM) and synovial fluid mononuclear cells of RA patients will be examined. In other studies, the synthesis of IgM-RF and anti-DNA antibodies by mononuclear cells of the spleen and bone marrow of MRL/1 mice and control strains will be quantitated, and factors regulating the synthesis of these antibodies will be examined. Efforts will also be made to increase the sensitivity of the available radioimmunoassay for IgG-RF so that it may be utilized for the quantitation of the synthesis of IgG-RF in cell cultures of human PBM and mouse spleen cells.